score = int(input('请输入一个整数：'))
degree = 'DCBAAF'
if score > 100 or score<0:
    print('wrong score.must between 0 and 100.')
else:
    index = (score - 60) // 10
    if index >= 0:
        print(degree[index])
    else:
        print(degree[-1])
        